摘要:

When silver (100) and (110) single crystals were sputtered by 160–200‐eV argon ions from an arc the well‐known spot patterns appeared when the sputtered particles were collected as a thin film on glass plates. To determine whether similar spot patterns would result from sublimation, the same crystals were sublimed at temperatures between 642° and 815°C under high‐vacuum conditions. Optical transmission densitometer measurements on the resulting thin films indicated that during sublimation the emission was approximately cosine, and no evidence of preferential ejection of silver particles during sublimation was detected. It is estimated that if preferential ejection is taking place along the close‐packed directions of the crystal during sublimation in this temperature range, this emission produced a thickness change of the collected silver films such that the transmitted light intensity varied from a cosinelike curve by less than 5% at those angles.

ISSN:0021-8979    

DOI:10.1063/1.1714601

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Using a conventional ballistic technique, magnetization curves of a superconducting Pb‐27% Tl alloy have been obtained from the transition temperatureTc=6.43°K down to 1.70°K. The thermodynamic critical field curve indicates that this alloy is of the strong coupling type. The Ginzburg‐Landau parameters deduced from several features of the magnetization curves are given and their temperature dependence is compared to theoretical models.

ISSN:0021-8979    

DOI:10.1063/1.1714602

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Dislocations in low dislocation density (∼102cm−2) single crystals of ZnWO4have been analyzed by the application of standard etching techniques and by Borrmann and Berg‐Barrett x‐ray diffraction techniques. The majority of dislocations lying on the (010) slip planes were found to have [100] Burgers vectors, while the remainder had [001] Burgers vectors. Dislocations lying on the (100) plane had predominantly [001] Burgers vectors; dislocations with [010] Burgers vectors were present, but uncommon. In Borrmann photographs dislocations which were close to the exit surface of the crystal gave images of increased, rather than decreased, intensity. The effect of the oxygen atom positions on the intensities of the anomalously transmitted x‐ray beams was shown to be significant in ZnWO4. Also, impurity segregation, which was revealed in both transmission optical and in x‐ray photographs, indicates that facetting occurred on a convex growth interface.

ISSN:0021-8979    

DOI:10.1063/1.1714603

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Both diffusional creep and sintering involve mass transport of the stoichiometric group of atomsA&agr;B&bgr;. The driving force in each case is external to the lattice, being applied mechanical stress in the case of diffusional creep and surface tension in the case of sintering. It is assumed that point defect mechanisms are involved in the diffusion process. Herring has considered the case of diffusional creep by lattice diffusion where charge effects are absent. The analogous case of creep by grain‐boundary diffusion, which becomes the important process at small grain size, has also been treated. [A. L. Ruoff, Materials Science Center Rept. No. 298, Cornell University, Ithaca, New York; and R. L. Coble, J. Appl. Phys.34, 1679 (1963)]. The diffusional creep of a polycrystalline specimen is here formulated exactly and terms which must be dropped to obtain Herring's expression (for either metallic or ionic crystals) are directly specified. It is then shown that Herring's equations apply to a pure ionic crystal when the conduction is purely ionic and space‐charge effects can be ignored if the tracer diffusion coefficientDin Herring's equations is replaced byDM, and the atomic volume &OHgr; in his equations is replaced by the molecular volumeVMof the diffusing ``molecule'' ofA&agr;B&bgr;. IfAatoms have the smallest tracer diffusion coefficientDTa0, thenDM=DTa0/fa&agr;, wherefais the correlation factor.

ISSN:0021-8979    

DOI:10.1063/1.1714604

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The effect of segregating a nonvolatile impurity during normal freezing in an off‐stoichiometric melt under constant component pressure is examined. A modified normal freeze equation is derived relating the impurity concentration in the solid to the fraction of original melt solidified for any off‐stoichiometric melt composition. The correction term in the modified equation becomes significant for segregation coefficients of the order of unity and melt compositions appreciably off stoichiometry.

ISSN:0021-8979    

DOI:10.1063/1.1714605

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Beam divergences were measured and far‐field patterns photographed for 37 ruby rods of different quality. The growth with pumping power of the most intense portion of the laser beam was measured for two rods of very different quality. An autocollimator reticle image was photographed after passage through each rod. Correlation of beam divergence with optical parameters is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714606

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

In the present paper, calculations have been made for the magnetic anisotropy developed in cold‐worked iron‐nickel alloys near the 75% Ni composition. The treatment is based on the slip‐induced directional order theory of Chikazumiet al.[J. Phys. Soc. Japan12, 1259 (1957)]. The theory states that in an ordered ferromagnetic solid solution (long‐ or short‐range order, or clustering), slip results in the creation and preferential alignment of distinct type(s) of atom pairs (e.g., Fe&sngbnd;Fe) which lead to an induced magnetic anisotropy. The important conclusion from this theory is that the direction of the induced easy axis of magnetization depends sensitively on the orientation of the deforming crystal and the geometry of the deformation process, as well as the type and degree of ordering in the alloy. The present treatment extends the original analysis for the case of rolling to single crystals of several new orientations: (110)[1¯12], (110)[1¯10], (111)[1¯1¯2], (112)[1¯10], and (112)[1¯1¯1]. These orientations, plus those studied by Chikazumiet al.((100)[001], (100)[011], and (110)[001]), contain the most likely operating slip systems whose slip directions are symmetrically disposed about the rolling direction and are hence more stable than others during rolling. Some of these orientations are important components of texture in recrystallized or cold‐rolled polycrystalline face‐centered cubic materials. In addition to the rolling analysis, calculations have been made for the anisotropy resulting from drawing of wires with ⟨111⟩ and ⟨001⟩ axial orientations. These two orientations are likewise prominent components of polycrystalline wire textures.The present work shows that drawing of a ⟨001⟩ wire induces a hard magnetic direction along the wire axis, while this axis becomes an easy direction if the orientation is ⟨111⟩. For rolling, except for the cases of (001)[100] and (110)[001] studied by Chikazumiet al., where the induced easy axis lies along the transverse direction, most other orientations generally place the easy axis along the rolling direction. This suggests a plausible explanation for the observation that the rolling direction becomes an easy axis of magnetization when a randomly oriented polycrystalline aggregate is rolled. This work also predicts that rolling of {112}⟨111⟩ and {110}⟨112⟩ textures (symmetrical variants included), which are prominent texture components in rolled Permalloy, results in an easy axis along the rolling direction. Suggestions for experimental testing of the theory are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714607

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Capacitance vs bias voltage data are presented for Au&sngbnd;KTaO3surface barrier Schottky diodes. Substantial deviations from the normal Schottky capacitance relationship have been observed and attributed to a field‐dependent dielectric constant in the depletion layer. From the capacitance data obtained at room temperature, &egr; vsEandPvsEcurves have been calculated for KTaO3and found to be consistent with previous measurements made using conventional techniques at 4.2°K.

ISSN:0021-8979    

DOI:10.1063/1.1714608

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Computed dispersion characteristics are presented for perpendicularly propagating electron cyclotron harmonic waves in an infinite plasma having a delta‐function transverse electron velocity distribution and an arbitrary longitudinal velocity distribution. It is shown that in general the propagation occurs in passbands centered on the cyclotron harmonic frequencies and that a given mode can carry positive or negative rf energy depending on the frequency and wavenumber. This suggests the possibility of growing waves in finite plasmas due to interaction with slow wave circuits. Even in an infinite plasma, as the ratio of plasma frequency to cyclotron frequency increases, modes in successive passbands couple to each other, leading to wave growth in time. This represents absolute instability of a type which may be closely related to effects observed in some thermonuclear fusion studies and other laboratory plasmas. There may also be important applications of these modes to the construction of practical microwave oscillators and amplifiers.

ISSN:0021-8979    

DOI:10.1063/1.1714609

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The use of orthophosphoric acid for the observation of etch pits in CdS thin films is demonstrated. From these studies, some suggestions as to the polarity and crystal growth processes in these thin films are put forward.

ISSN:0021-8979    

DOI:10.1063/1.1714610

出版商:AIP    

年代:1965

数据来源: AIP